1. Field of the Invention
The present invention relates to heat exchangers. More specifically, the field of the invention is that of fin geometries for use in conjunction with heat exchanger tubes.
2. Description of the Related Art
Heat exchangers are used in air conditioners and heat pumps to transfer energy between two fluid mediums, e.g., a refrigerant fluid and ordinary air. The refrigerant fluid is circulated through relatively small diameter tubes and air is passed over the surface of the tubes so that heat may be transferred from the refrigerant fluid, through the material of the heat exchanger tube, to the air. Thin metal sheets, or fins, are attached to the heat exchanger tubes to provide a greater amount of surface area to contact the air and thereby enhance the heat transfer. The fins include receiving apertures so that the metal material of the fins is securely held in thermal contact with the material of the tubes. By the forced convection caused by the fan system, heat is transferred from the fin material to the circulating air. By the thermal contact with the tubes, the fins conduct heat between the externally circulating and air and the refrigerant fluid in the heat exchanger tubes.
To enhance the transfer of heat through the fins between the air and the refrigerant fluid, the fins have surface enhancements that accentuate the turbulence and mixing of the air around the heat exchanger. For example, the inventor's previous U.S. Pat. No. 4,691,768, entitled "LANCED FIN CONDENSER FOR CENTRAL AIR CONDITIONER", assigned to the assignee of the present invention, the disclosure of which is incorporated by reference, discloses one such enhanced fin design. In this design, the fins are generally corrugated and have locally parallel pairs of lanced bridge-like formations which increase flow turbulence and flow mixing. However, such corrugated designs are more difficult to manufacture than flat plate designs.
Other corrugated fin designs also provide improvements in the heat exchange efficiency of fins. One prior art design involves louvered convolutions with staggered rows of tube holes being located on the ridges of the convolutions. Another prior art design involves a fin having three sets of offset, inclined louvers above and below the fin plate. Yet another prior art design involves a radially symmetric fin design for bi-directional air flow. Other prior art fin designs call for troughs and crests for enhancing heat transfer, stepped louvers, louvers of unequal length, and fins with a corrugated surface having local air guidance profiles.
A flat plate design which provides heat transfer characteristics similar to that of the enhanced corrugated type design is shown in FIGS. 1 and 2. Fin 20 is made of thin sheet metal, approximately 0.0044 inches thick, and has a nine section louver arrangement between adjacent heat exchanger tube collars 22. The fins of the heat exchanger are separated by the height of collar 22, with the top of one fin collar abutting the bottom of the adjacent fin collar. The nine section arrangement shown in FIGS. 1 and 2 may be efficiently manufactured in a one step enhancement station within the overall die stamping process. This type of design has gained widespread acceptance because the heat transfer efficiency of the fin is comparable to that of other enhanced corrugated fins, relatively easy to manufacture, and structurally sound.
Fin 20 includes outer edge louvered portions 24 which have outer portions extending in a plane generally coincident with the plane of fin 20. The interior facing portions of edges 24 are bent downwardly in the direction of center element 26 which is located in the middle of fin 20. The middle of center element 26 is generally disposed in the plane of fin 20 and its edges are bent upwardly. Three louvers 28 are disposed between center element 26 and edges 24. Louvers 28 are generally disposed at an angle in the range of 23.degree. to 27.degree. relative to the plane generally defined by fin 20, with their center axes being generally coplanar with the plane of fin 20. Also, the outer most louvers 28 are divided in half by flat portions 30, with additional flat portions 32 extending around collars 22 and to the outer edges of fin 20 to separate groups of louvers 28.
These fin structures are required to be both cost effective and efficient. However, often a more efficient design proves to be more expensive in terms of materials and/or manufacturing. Conversely, relatively simple designs tend to be less desirable because of inferior heat transfer characteristics. Therefore, a more efficient and economically viable heat exchanger fin design is desired. Also, it is desirable to minimize material costs by using thinner sheet metal, as conventional designs are already made with sheet metal which is as thin as practical.